这个圆的直径是十厘米。

Zhè gè yuán de zhíjìng shì shí límǐ.

The diameter of this circle is ten centimeters.

这棵树的树干直径已经有三十多厘米了。

Zhè kē shù de shùgàn zhíjìng yǐjīng yǒu sānshí duō límǐ le.

The trunk of this tree already has a diameter of more than thirty centimeters.

要计算圆的面积，首先得知道它的直径或者半径。

Yào jìsuàn yuán de miànjī, shǒuxiān děi zhīdào tā de zhíjìng huòzhě bànjìng.

To calculate the area of a circle, you first need to know its diameter or radius.